Kenwood TKR-851 Service Manual

Also see for TKR-851: Function reference Programming reference Modification Information Brochure & specs Instruction manual

TKR-851144. PLL Frequency SynthesizerThe PLL frequency synthesizer circuit consists of the fol-lowing circuits : 4-1 receiver PLL circuit, 4-2 transmitter PLLcircuit, and 4-3 unlocked detector circuit.4-1. Receiver PLLThe receiver PLL circuit is located in VCO unit A3 (X58-480) on TX-RX unit (X57-696 A/2), and consists of VCXO X2,VCO’s (Q350 and Q351), a single-chip PLL IC IC300, bufferamplifier Q355, and high-frequency amplifier Q302.The VCXO generates 16.8MHz. The frequency stability iswithin ± 1.5ppm (Temperature range of –30 to +60°C). Thefrequency tuning of the VCXO is done to apply a voltage topin 1 of the VCXO. The output of the VCXO is applied to pin 8of the PLL IC through the pin 7 of the VCO.The first local oscillator is a lower heterodyne local oscilla-tor, and the VCO oscillator frequency is 405.15 to 435.15MHz(K), 395.15 to 425.15MHz (E).The oscillator frequency is controlled by applying the VCOcontrol voltage, obtained from the phase comparator to thevaractor diodes.4-2. Transmitter PLLThe transmitter PLL circuit is located in VCO unit A2 (X58-481) on TX-RX unit (X57-696 A/2), and consists of VCXO X3,VCO’s (Q350), a single-chip PLL IC IC300, buffer amplifierQ355, and high-frequency amplifier Q302.The VCXO generates 16.8MHz. The frequency stability iswithin ± 1.5ppm (Temperature range of –30 to +60°C). Thefrequency tuning and modulation of the VCXO are done toapply a voltage to pin 1 of the VCXO. The output of the VCXOis applied to pin 8 of the PLL IC through the pin 7 of the VCO.The VCO oscillator frequency is 450.00 to 480.00MHz (K),440.00 to 470.00MHz (E).The oscillator frequency is controlled by applying the VCOcontrol voltage, obtained from the phase comparator to thevaractor diodes.4-3. Unlock Detector CircuitIf a pulse signal appears at the LD pin of IC300, an unlockcondition occurs, causing the voltage applied to the pin of themicroprocessor to go low. The names of this pin are LDT forTX PLL and LDR for RX PLL. When the microprocessor de-tects this condition, the transmitter is disabled.Q351VCO unit (X58-480)SRRVCO AIC300VCO BQ355Q350Q354Q352Q353Q300 Q302VCXOX2TX-RX unitIC604SWSWSWAMPAMPLPF PLL-ICμ-comCP,DPEPR,LDRVCO unit (X58-481)VCO AIC300Q355Q350Q300 Q302VCXOX3TX-RX unitIC604AMPAMPLPF PLL-ICμ-comCP,DPEPT,LDTMOMOMOFig. 5 Receiver PLL Fig. 6 Transmitter PLLVCO A : 450~480 (K)440~470 (E)Top viewTX VCO(X58-481)VCO A : 440~460VCO B : 460~480RX VCO(X58-480)(MHz)–44.850–44.850Fig. 7 VCO oscillation frequencyCIRCUIT DESCRIPTION